I use these on a regular basis. Your code should look like this...
private const BEVEL:BevelFilter = new BevelFilter(4, 90, COLOR2, 1, COLOR2, 1, 10, 10, 1, 1, "inner", true);
That second-to-last argument accepts a string.
Not sure why the docs represent it differently. This was off of the code hints for Adobe Flash CS6, and I know this should work.